Electrical fuse and heater units



March 1-0, 1970 HINGORANY ET AL 3,500,276

ELECTRICAL FUSE 'AND- HEATER UNITS Filed Oct. 25, 1967 4 Sheets-Sheet 1March 10; 1970 A. R. HINGORANY ETAI- 00,

ELECTRICAL FUSE AND HEATERZUNITS 4 Sheets-Sheet 2 Filed Oct. 25, 1967FIG.3.

FIG.4.

A. R. HINGORANY ET AL ELECTRICAL FUSE AND HEATERUNITS Filed Oct. 25,19.67

FIGS

' /I/I/I/ 4 Sheets-Sheet 5 March 1-0, 1970 A. R. HINGORANY ETAL3,500,276

ELECTRICAL FUSE AND HEATER 1mm 4 Sheets-Sheet 4 Filed Oct. 25. 1967 FIG]United States Patent 3,500,276 ELECTRICAL FUSE AND HEATER UNITS Ashok R.Hingorany, Pawtucket, R.I., and Joseph A.

Willoughby, Attleboro, Mass, assignors to Texas InstrumentsIncorporated, Dallas, Tex., a corporation of Delaware Filed Oct. 25,1967, Ser. No. 678,053 Int. Cl. H01h 85/02 U.S. Cl. 337-183 2 ClaimsABSTRACT OF THE DISCLOSURE A comparatively thick stiffening and in somecases deformable metal backing layer, which may also be thick enough tofunction as a substantial heat sink, has bonded thereto a comparativelythin etch-resistant electrically insulating polymer layer. Aluminum isused for the backing layer when corrosion is to be minimized. On thepolymer layer is bonded a comparatively thin metal layer of conductivefuse-forming material or in the alternative conductiveresistance-heating material. The prebonded layers and their bondedcomposite are preferably in strip or sheet form. The thin conductivelayer may be adhered as a sheet or formed in situ as a sheet by platingon the insulating layer. The. conductive layer in its position on theinsulating layer is converted to form individual or groups of individualfuse or heater patterns as part of the composite. This is accomplishedby printing etch-resistant patterns on the conductive layer byphotographic, silk-screen or like printing. The conductive layer is thenetched to remove all of its conductive material outside of the patterns,leaving the latter intact as fuse or heater elements. The backing andinsulating layers of the composite are then segmented by shearing,cutting or the like along lines to form individual electrical units,each supporting one or more fuse or heater elements. The individualunits may be formed into curved shapes or left flat for convenient usein making connections with line terminals or to form heater walls, asdesired. The fuse units are shaped as polygons or the like and carryidentical single fuse elements or groups of identical fuse elementscarried on one or both sides and having terminals on different straightsides of the polygon. Thus by rotation the identical or grouped fuseelements may be substituted one for the other in a set of line terminalclips of a circuit served by the fuses.

Heretofore fuses have been variously complexly constructed, as forexample with metallic terminal cups joined by a fragile fuse wiresurrounded by a protective glass sleeve carried by the cups. Circuitrywithout fuses or heaters has been constructed on what are called circuitboards made by printed and etched circuitry applied directly toinsulating boards or ceramic platens. In some cases an individual boardof this type carrier an individual fuse element (see U.S. Patent2,941,059). However, the insulating board form was subject to warping,abrasion and spontaneous disintegration, and the ceramic form was quitefragile. Neither of them could be bent to desired fuse or heater shapes.Moreover, none of these incorporating any fuse or heater elementsprovided any effective heat sink, as in many cases is desirable. In thecase of heater constructions it has heretofore been costly and clumsy toget them into close efficient heat-exchange relationship with heatingpanels, composite thermostatic sheets and the like which are served bythe heaters.

Advantages of the invention are reduction in volume and Weight of theunits and therefore reduction in costs of raw materials. The method oftheir manufacture favors rapid quantity production and therefore lowlabor costs. More accurate circuit values may be obtained along with"ice a high degree of design flexibility. Fuses may be designed forreliable applications to locations having higher temperatures and/orcorrosive ambient conditions. Heaters may be more closely organized withheating panels, thermostatic composites or the like which they serve.Expended fuses or damaged heaters are. more apparent visually. The unitsare very compatible with electrical systems employing conventionalprinted circuit boards. Other objects and features will be in partapparent and in part pointed out hereinafter.

Referring to the accompanying drawings:

FIG. 1 illustrates one form of a fuse made according to the invention;

FIG. 1A on a reduced scale illustrates how a unit such as shown in FIG.1 is made;

FIG. 2 illustrates a bent variation of the FIG. 1 form;

FIG. 3 is a plan view of a multiple twin fuse unit made according to theinvention, a small portion of certain layers being broken away;

FIG. 4 is a plan view of a line terminal block for accepting the unit ofFIG. 3, as shown by the broken dart;

FIG. 5 is an enlarged cross section taken on line 55 of FIG. 4 andillustrates one of the line terminal clips in the terminal block;

FIG. 6 is a plan view of a quadrated form of a multiple fuse unit;

FIG. 7 is a view like FIG. 6 illustrating a modification of thequadrated form of unit.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings. The drawings are not to aproportional scale, the thicknesses of various layers having beenexaggerated for clarity.

Referring to FIG. 1, numeral 1 indicates a metal back ing lever whichforms a sufficiently stiff support for normal handling of the finishedfuse in placing it in, and removing it from, circuitry. However, undersufficient force applied during manufacture it is bendable duringmanufacture as illustrated in FIG. 2. It may be single-ply or multiply.Any appropriate metal may be employed such as, for example, steel,copper, or aluminum if atmospheric corrosion is to be resisted. In casesrequiring it the back layer is made thick enough to constitute a goodheat sink. Appropriate thicknesses for the backing layer are in therange of twenty to fifty mils, with about twentyfive mils preferred. Thegreater thicknesses are appropriate in those cases in which the backinglayer is to function as a heat sink.

Attached to one face of the metal back is an etchresistant insulatinglayer 3 composed of a polymer. The polymer material may be Teflon-coatedKapton. Teflon is a fluorocarbon and Kapton is a polyimide, both beingtrade names of the E. I. du Pont de Nemours & Co. The Teflon forms agood bond under heat and pressure. Mylar may be also used but requiresattachment by one of the usual adhesives for such purposes. Mylar isalso a Du Pont trade name. Kapton may also be used without the Teflonand attached by means of a similar adhesive. An appropriate range ofthicknesses for the insulating layer 3 is two to sh; mils with about twomils preferred.

0n the polymer layer 3 is a flat fuse element consisting of a calibratedlink part 5 having terminal portions 7. The metal composing the fuseelement is any of those well known for the purpose, including zinc,copper, alloys such as those composed of bismuth, lead and tin, etc. Thefuse element is What is left after a layer of conductive materialattached to the top of the polymer layer 3 has been etched away, as willappear. Appropriate thicknesses are in the range of two to twelve milswith three mils preferred. The shape of the fuse may be varied asdesired, for example to include a shunt portion.

In FIG. 1A is illustrated a rapid method by which fuses made accordingto the invention may be constructed. This figure shows a sheet in stripform of starting backing material 1M from which backings such as 1 aremade. To this strip is bonded in the manner above described a sheet instrip form 3M which provides the starting material to form insulationsuch as 3. To the strip 3M is bonded, by plating or in strip form, fusematerial 5M which provides the starting material from which fuseelements such as 5, 7 are obtained. It is to be understood that the termbonded layer for layer 5M includes a plated-on layer and a strip form oflayer. The composite C is formed under heat and pressure, as required,by pressure rolling or in a platen type of press. The layered assembly1M, 3M, 5M may be referred to in general as a starting composite.

The composite is converted to form fuse elements such as 5, 7 byprinting etch-resist patterns on the conductive layer 5M byphotographic, silk screen or other appropriate printing process. In thephotographic process, by the development of the print formed in aphotosensitive film on layer 5M, such a print is converted intoinsoluble etch-resist material. Unprinted portions being soluble arewashed away. In the silk-screen process the print is applied directly inetch-resistant form. Photoresist patterns thus applied are illustratedin FIG. 1A by stippled areas R outlined on the layer 5M of composite C.Then by etching the layer 5M its portions not outlined are dissolvedaway leaving for example fuse elements 5, 7 such as shown in the lowerright in FIG. 1A. Then by shearing or cutting along dotted lines such asindicated at S individual fuse elements 1, 3, 5, 7 are produced such asshown in FIG. 1.

The dots D on the tab 7 in FIG. 1 indicate where circuitry may beattached by anyone of conventional means such as welding, soldering orany other appropriate means. It may be mentioned that when the layer 1is made thick enough to act also as a heat sink to prevent overheatingand change of calibration of the link portion 5, that this also preventsdestruction of any soldered connections at D.

In FIG. 2 there is shown on a reduced scale a unit such as 1, 3, 5, 7such as shown in FIG. 1 but bent during manufacture to a partiallytubular form. This again has a stiff metal backing in the form of a tube9 on the outer surface of which is a curved layer 11 of the insulatingpolymer. Axially disposed on the tube is the calibrated conductive linkportion 13 terminated by curved end tabs 15. The tabs may be inserted inthe usual way into and removed from the usual line terminal spring clipsto replace conventional cylindrical type glass housed fuses. Two areasof the fuse shown at 17 are nonconductive and form convenient places formanipulation by the fingers or pliers.

In FIG. 3 a form of the invention is illustrated in which a square,metal backing plate 29 shown at a broken-away portion carries theinsulating polymer layer 31 upon which is the etched printed circuitryobtained as above described. In this case the circuitry constitutes twoseparate but identical banks P, Q of circuit arrangements having tenfuses each, numbered 33. From each fuse are two leads extending tothirteen marginal terminal portions 35. Various groups of the fuses havecommon grounds as shown.

At numeral 37 is shown a line terminal block for thirteen circuit lines39 having thirteen springy line terminal clips 41, as illustrated inFIGS. 4 and 5. The clips 41 are located on the bottom of a socket 42 inthe terminal block 37. The side of one half of the composite fuse blockas shown in FIG. 3 is inserted into the terminal block 37 as shown inFIG. 4. The terminals 35 engage the line terminal clips 41 respectively,which places the lower half of the fuse block into circuit. At this timethe upper half of the block extends above the terminal block 37 and actsas a dead standby. If and when one of the fuses 33 blows, the user mayextract the fuse block from the terminal block 37, turn it over andinsert the inverted upper half into block 37. This restores all of thecircuits. If desired a layer such as 31 with circuitry 33 and 35 thereonmay be carried on the other side of the backing plate 29 to supplyadditional replacement circuits.

While it might appear that it would be wasteful to remove good unblownfuses from circuitry just because one, or less than all, has blown, thisis not the case because of the economical construction, both inmaterials used and the manufacturing cost.

In FIG. 6 is shown in plan view a square multiple fuse block made in themanner which will be readily understood from the above descriptions. Inthis case the independent fused circuitries are quadrupled and placed inquadrature, as shown. Thus the FIG. 6 block numbered 43 has fourquadrants 45 each of which carries three etched patterns forming threefuses 47 with their leads 49 extending to marginal tab portions 51. Ifthe current and voltage in any two adjacent circuits are such as mightcause leakage of current and/or heat between them across the insulatorlayer 46, then block 43 may be punched out as illustrated at numerals53. The form of the multiple fuse blocks shown in FIG. 6 may be used inconnection with a suitable terminal block to make four fuse replacementsin a circuit.

In FIG. 7 is shown a form of the invention like that shown in FIG. 6,except that in this case holes such as 53 are omitted. In this form asecond polymer insulating layer 55 is bonded on the upper surfaces ofthe polymer layer 46 and the fused circuits. This prevents electricalleakage or excessive communication of heat between any two circuits onthe entire board.

In both the FIG. 6 and FIG. 7 forms the back surfaces may have circuitryrepeated thereon, as above described in the case of FIG. 3. Also, inboth of these FIGS. 6 and 7 forms of the invention are shown a hole 57through the device by means of which it may be anchored by a suitablebolt or the like when in position in a terminal block. This preventsvibration or the like from ejecting the device from the terminal block.

It is further to be understood that a polymer layer may be applied tocover fuse or heater circuitry so that a unit would have a metal base, apolymer insulator thereon, a heater or fuse pattern on this polymer, anda protective polymer layer covering the heater or fuse pattern.

Highly accurate circuit values may be obtained, especially when aphotographic process is used, because then the original art work for therequired patterns may be made quite large. Any errors in such work areminimized by the photo-reduction to the actual pattern size precedingetching. Thus the accuracy in the ultimate scale to which the fuses aremade has been found to be on the order of about ten times that of themaster drawing accuracy.

The advantage of the metallic backing, when made thick enough to providea heat sink, minimizes the deviation from the calibration of a fuse whenoperating under excessively high temperature. Heavy duty fuses willsometimes burn out under temporarily hot conditions when the current inthe circuitry does not call for it. By the use of a thick enough metalbacking as part of the fuse, heat may be abstracted from the printedcircuitry to forestall this trouble. Fuses, and more particularly thosefor light duty and high accuracy of calibration and operating underconditions of ordinary temperatures, should in general be constructedwith a backing layer such as 1 which will not supply much heat sinkeffect but only rigidity. Otherwise the heat sink effect may destroy theaccuracy of calibration.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above constructions and methodswithout departing from the scope of the invention, it is intended thatall matter contained in the above description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

What is claimed is:

1. An electrical fuse unit comprising electrically insulating sheetmaterial arranged substantially coextensive with and bonded to a stifflayer of metal sheet material, and a plurality of groups of electricallyconductive fuse elements of selected thickness bonded to said insulatingsheet material in spaced, electrically insulating relation to eachother, each of said fuse elements having a pair of terminal portions ofselected width electrically interconnected by an intermediate fuseportion of relatively smaller width fusible in response to the passageof selected electrical current therethrough, said groups of fuseelements being arranged adjacent respective identical edges of saidinsulating sheet material, said terminal portions of said fuse elementsin each group being located in spaced relation to each other along anedge of said insulating sheet material commonly adjacent thereto forforming a plurality of fuse circuits extending between spaced locationsalong said commonly adjacent edge of said insulating sheet material.

2. An electrical fuse unit comprising a layer of electrically insulatingsheet material having a plurality of substantially identical sheetedges, a stiff backing layer of metal sheet material arrangedsubstantially coextensive with and bonded to one sheet surface of saidinsulating layer, and a plurality of groups of electrically conductivefuse elements of selected thickness bonded to an opposite sheet surfaceof said insulating layer in spaced, electrically-insulating relation toeach other, each of said fuse elements having a pair of terminalportions of selected width electrically interconnected by anintermediate fuse portion of relatively smaller width fusible inresponse to the passage of selected electrical current therethrough,said groups of fuse elements being arranged adjacent respectiveidentical edges of said insulating layer, said terminal portions of saidfuse elements in each group being located in spaced relation to eachother along said insulating layer edge commonly adjacent thereto forforming a plurality of fuse circuits extending over said insulatinglayer between spaced locations along said commonly adjacent edge of saidinsulating layer.

References Cited UNITED STATES PATENTS 3,445,798 5/ 1969 Lohrmann337-227 3,416,114 12/1968 Bernutz et al 337-293 2,326, 257 8/ 1943Schmidt 337-166 3,401,369 9/ 1968 Palmateer et 211.

2,934,627 4/1960 Bristol et a1 337-293 2,941,059 6/1960 Sims et a1.337-187 3,161,457 12/1964 Schroeder et al.

3,266,661 8/1966 Dates 219-438 X 3,354,542 11/1967 Mallia 337-4163,297,846 1/1967 Peltier 337-416 H. B. GILSON, Primary Examiner US. Cl.X.R. 337-187, 293,

